When a switching element such as a power semiconductor module is switched off, a spike-like surge voltage is generated. When the surge voltage is large, there is a risk of causing a short-circuit breakdown of the switching element. Conventionally, there is disclosed a technique in which, by connecting snubber capacitors and semiconductor modules with metallic bars having a relatively high conductivity and wiring on the substrates, the impedance components between the snubber capacitors and the semiconductor modules are made lower, to reduce the spike-like surge voltage that flows when the switching element is switched off, and, for adjacent semiconductor modules, by equalizing the wiring length between the snubber capacitors, the impedance components for respective semiconductor modules are made substantially equal, which results in equalization of protection effects from a surge voltage among the respective semiconductor modules (for example, Patent Literature 1).